Heat exchanger element



March 22, 1966 T. F. PAULS 3,241,608

HEAT EXCHANGER ELEMENT Original Filed Dec. 29, 1955 1 2 Sheets-Sheet 1 lllllll l 1 INVENTOR. 77 THERON F PA ULS FIG-6 MW March 22, 1966 1-. F. PAULS HEAT EXCHANGER ELEMENT Original Filed Dec. 29, 1955 2 Sheets-Sheet 2 FIG '8 INVENTOR. THE/PON F PA UL 5 fm/gww A T TO/PNEY United States Patent 3.241.608 HEAT EXCHANGER ELEMENT Theron lF. Pauls, Godfrey, IlL. assignor to Olin Mathieson Chemical Corporation, East Alton, ill., a corporation of Virginia Original application Dec. 29, 1955, Ser. No. 556,225. now Patent No. 3,206,838, dated Sept. 21, 1965. Divided and this application Nov. 8, 1%3, Ser. No. 327,571

1 Claim. (Cl. 165--177) This application is a division of copending application Serial No. 556,225, filed December 29, 1955, now United States Patent 3,206,838.

This invention relates to a heat transfer device and more particularly to a heat exchanger tube having integral fins.

It is desirable that heat exchange tubing for boilers, refrigerators, condensers and the like he provided with external fins. Such heat transfer fins are usually brazed or soldered on the tubing except where the tube structure is very heavy and permits the fins to be cast, extruded, or rolled. However, especially where the tubing is of the flat or oblong sheet metal type, thin walled tubing and the fins are usually brazed or soldered together. This is not only expensive and time consuming, but frequently fails to result in a rigid and efiicient joint. Generally, a brazed or soldered joint is of reduced heat exchange efficiency for lack of unimpeded heat transfer through the joint. Another heretofore known method of forming fins is a helical rolling method which, however, has the disadvantage of requiring a fully formed round tube blank together with an internal mandrel and which has the further disadvantage of requiring a considerably thick tube wall and complicated apparatus and controls for the proper extension of integral fins. This prior method is not readily adapted to formation of fins in conjunction with relatively thin sheet metal walls.

One object of this invention, therefore, is to provide a simple, low cost but improved design of finned heat exchanger tube. Another object is to provide a thin walled, relatively flat, sheet metal tube having a plurality of integral fins on the external surface of the tube for improved heat transfer efficiency. Another object is to provide an improved method of making a tubular form of heat exchanger unit having an extended heat transfer surface. Still another object is to provide a method adapted to high speed mass production of finned tubing from sheet metal.

Other objects and advantages will be evident from the following description of a preferred embodiment of this invention when taken in connection with the accompanying drawing in which:

FIG. 1 is a plan elevational view of a typical portion of one embodiment of the tubing;

FIG. 2 is a cross sectional view taken on line II-II of FIGURE 1;

FIG. 3 is a perspective View of the tubing of FIGURE 1 with portions broken away and shown in section on line IIIIII of FIGURE 1;

FIG. 4 is a cross-sectional view of another embodiment shown between the platens of apparatus used in its manufacture;

FIG. 5 is a semi-diagrammatic, elevational view showing the process of manufacturing tubing in accordance with this invention;

FIG. 6 is a plan view taken on line VI-VI of FIG- URE 5 showing a portion of the apparatus and material in the process of FIGURE 5;

FIG; 7 is a fragmentary view in cross section showing a fiat uninflated tube sheet between grooved die platens suitable for manufacturing the embodiment of FIG- URES l, 2, and 3;

FIG. 8 is a fragmentary view in cross section showing a fiat uninflated tube strip in a die arrangement suitable for manufacturing the embodiment of FIGURE 4;

FIG. 9 is a partial elevational view showing a portion of a radiator core including the finned sheets of this invention;

FIG. 10 is a fragmentary view showing another form of heat exchanger using the element of this invention; and

FIG. 11 is a semi-diagrammatic representation of portions of swaging rolls capable of forming the finned strip of the elements shown in FIGURE 10.

The foregoing objects are achieved in accordance with this invention by providing a novel method of forming a new type of finned tubing characterized by a relatively thin walled structure compared to the extension of the fins. The present invention is especially adaptable to manufacture of integrally finned tubing from a flat, collapsed but inflatable tube blank. It is: contemplated, according to this invention, that the exterior surfaces of an elongated, double walled, sheet metal blank be provided with transversely and longitudinally extending fins together with intervening wall portions of extreme thinness supported adequately by the fins. An elongated tube blank is provided having double walls, the opposed interior surfaces of which are contiguous but separable except at peripheral portions such as the lateral edges which are joined or bonded together in any suitable manner but preferably by pressure or roll welding and this blank is then subjected to deformation to simultaneously thin the opposed tube walls and elevate the fins from the material of the walls. Adherence preventing conditions are maintained during the deformation operation while the fins are being forged or swaged from the sheet material of the walls which are preferably of sheet metal. It is also preferred that adherence preventing material be maintained at the interface between the opposed Walls during the fin forming operation.

Except for the longitudinally extending fins at the lateral edges of the tube blank, the fins formed are preferably transverse and of greatest outward extension between and remote from the lateral edges of the elongated sheet unit and of least extension adjacent one or both of the lateral edges. This fin shape is of advantage both during and after erection of walls of the finished tubing.

At this stage, the tube blank characterized by extreme thinness between fin extension, is adapted to generation of a tubing passageway by fluid inflation especially where the fins are tapered down at the lateral edges. Following inflation there is produced a new type of sheet metal tubing of extreme wall thinness together with considerable fin extension. Although the tube blank may be opened or inflated to any suitable cross sectional shape, it is preferably formed by inflation to relatively flat or oblong shape. The tubing, when of flat or oblong shape, preferably has a series of transverse fins extending between the opposed lateral edges forming longitudinally extending fins or ribs. Thus, it is contemplated that seamless, relatively flat or oblong tubes be provided with integral transverse ribs or fins by swaging or forging while in the collapsed or uninflated condition after which the tube wall is erected to provide an internal fluid passageway.

It is further contemplated that the finned tubing be formed in such a way that the lateral edges are pres sure bonded or roll welded together simultaneously with the forging or swaging of the fins. This can be accomplished with suitable rolls so that while the fins are being formed the lateral edge portions are being integrated.

The special finned tube of the illustrative specific embodiment shown in FIGURES 1, 2 and 3 consists of first side wall 1, the opposite side wall 2, both of which are integrated or preferably joined together by pressure welding at the lateral edges 3 and 4 so as to form at these lateral edges a unitary structure completely sealed together and requiring no extraneous brazing or welding materials. Side wall 1 bears a series of external fins 5, while side wall 2 bears corresponding external fins 6. The fins are integral with the tube walls. It is to be noted that in the medial section of side walls 1 and 2, these side walls are extremely thin between the fins and 6, respectively. This makes for more efiicient and improved heat transfer through the side walls and to the fins. At the lateral edges 3 and 4, the thickness of the structure is considerably greater than that of the side walls. This makes for improved longitudinal rigidity and ruggedness of structure.

Pins 5 and 6 are of greater extension at a point intermediate their ends. It is to be noted, for example, that fin 5 is of greater extension at the midpoint 7 than at its ends 11 and 9. Likewise, each fin 6 on the other side is of greater extension at midpoint 8 than at the end portions 10 and 12. This construction provides not only improved heat exchange but also needed rigidity at the thinnest portions of the walls 1 and 2 and enables them to better resist distention under high internal pressure. Thus desirable increase in fin extension is produced together with a desirable thinness of intervening tube wall. The two in conjunction make for most efiicient heat transfer. The single fluid passageway 13, generated by bulging of the walls 1 and 2 in any suitable way but preferably by inflation, is of lenticular shape in general. The shape of this passageway, however, can vary from the extremes of an ovoid shape to a rather flat oblong or nearly rectangular shape.

The fins of the embodiment of FIGURES 1, 2 and 3 can be formed with apparatus as shown in FIGURE 7 where is the working end of an upper forging die and 16 is the working end of a lower forging die. These operate upon special fiat, laminated stock 200 having the opposed component layers 201 and 202 joined at their lateral edges at 19 and but maintained in separation at 12 between these lateral edges in any suitable manner while in contiguity. For example, at 12 there may be provided a thin layer of any suitable weld or adherence preventing material.

Die block 15 is provided with a series of grooves between protruding. lands 17. In similar manner, die block 16 has a grooved working face provided with a series of spaced lands 18 in registry with the lands 17 of block 15. Each of the lands or teeth 17 and 18 are shaped in this embodiment by tapering lengthwise to be of greatest protrusion, which is to say closest approach, adjacent their midsections with respect to the corresponding opposing land. This die face arrangement works the greatest deformation of component sheets 261 and 202 adjacent the longitudinal midplane of the special completely annealed blank 260 and provides the greatest extension of the fins 5 and 6 (FIGURE 3). These are produced as an integral part of the tube as the forging dies 15 and 16 are brought into engagement with the blank 200 with desired pressure or impact. The resulting uneven deformation of the blank produces the integral fins 5 and 6 tapered down at ends 9 and 11 and 10 and 12 as shown in FIGURES 1, 2 and 3. Lateral edges 19 and 20 of the blank 2% are either left of original thickness or increased somewhat in thickness. Inasmuch as the greatest deformation is produced uniformly along the longitudinal midsection of the blank, the metal at this section is given the greatest work hardening effect while the metal adjacent the lateral edges is relatively soft and adapted for permitting inflation of the blank between any suitable known sizing dies or platens or for permitting bulging with a suitable mandrel. When the blank, now not only internally laminated but also externally finned, is of very long length,

it is preferably bulged by injection of inflation fluid pressure between sizing platens to give desired longitudinal uniformity of erection of the walls 1 and 2 and generation of the internal passageway 13.

The embodiment of the tube structure of this invention shown in FIGURE 4 is characterized by a streamlined or tear drop cross sectional configuration. In this embodiment, the finished tube consists of side wall 31, which bears a series of external fins 35, and the opposing side wall 32, which bears a similar series of external fins 36. These fins are of greatest outward extension adjacent the leading lateral edge 34 of this embodiment of the tube. Thus, the leading edge 37 of fins and the leading edge 38 of fins 36 protrude considerably to form a generous rounded streamlined leading fin section. Adjacent the trailing lateral edge 33 of the tube, the fins 35 and 36 are tapered down to merge gradually into the opposing side walls 31 and 32, which as in the previous embodiment are integrated at both the edges 34 and 33.

This embodiment of FIGURE 4 can advantageously be formed from the special blank 3% in the apparatus shown in FIGURE 8, after which the structure is inflated to the final finished form shown in FIGURE 4 between the spaced sizing platens 39 and 40 (FIGURE 4) the working faces of which are closely spaced adjacent the trailing end 33 and more remotely spaced adjacent the leading edge 34. First of all, however, special flat blank 360, preferably in completely annealed condition, is placed in the die cavity of the block 56 (FIGURE 8) where it is supported upon the grooved working face of the lower movable forging ram 56, also nested in the cavity of the block 50. Upper forging ram or die 55 is movable into the cavity of block and is adapted together with lower ram 56 to subject blank 300 to forging or swaging action. It is to be noted that in the apparatus of FIGURE 8, as contrasted with the apparatus of FIGURE 7 the lateral edges of the blank are confined, thus edge 333, which will form trailing edge 33 of the finished tube, and also edge 334- of the blank 300, which will form the leading edge 34 of the tube are confined in the cavity of the die block St The working faces of the forging rams and 56 are provided with a series of spaced teeth or lands 57 and 58, respectively. These, it will be noted, are located only adjacent edge 334 and the adjoining portion of the internal lamination or interface of separation 312. But adjacent the other edge 333 of the blank, forging lands 57 and 58 are tapered back so as to accomplish less firming and resultant forging of the blank 300. Thinning and forging in this embodiment is accomplished all the way to the outer periphery of the lateral edge 334. It will be understood, that with suitable symmetry in the blank 300, the forging lands 57 and 58 may extend uniformly all the way across the working face of the forging rams 55 and 56, respectively, to provide fins substantially completely across the tube structure as, for example, shown in FIGURE 10.

Upon completion of the forging operation, blank 300 now provided with a series of external fins on both sides, is then placed between suitably separated platens 39 and 40 (FIGURE 4) and subjected to internal inflation pressure so as to produce the shape of the finished tube shown in FIGURE 4 having the fluid passageway 43.

In any event, and for the production of the foregoing or any other embodiments, there is provided a flat twowalled blank in any suitable manner. Such may be formed by rolling or drawing a relatively thin-walled tube shut. Also the blank may be formed by extrusion after which the extruded blank may be flattened either by rolling or passage through a sizing or drawing die. If naturally occurring oxide within the interior of such a blank is insufficient for the purpose, an adherence preventing coating may be applied to the interior of the blank so as to prevent undesired sticking between the opposing walls of the blank during the rolling, drawing or the subsequent forging operation described herein. However, a preferred mode of providing the blank is to bring two strips of relatively thin materialinto superposition with an intervening layer of weld 01' adherence preventing material between the component sheets except at the lateral edges and then subjecting the superposed assembly to sufl'icient deformation to accomplish pressure welding of the lateral edges of the assembly. This blank is then suitable and ready for swaging or forging to form the desired finned tube structure.

An illustrative example of a process for making a finned tube blank in accordance with this invention is shown in FIGURES 5 and 6. The finned blank 79 produced is ready for erection to the final finished hollow form. As shown in FIGURE 5, long, relatively narrow component strips 61 and 62 are paid off from coils 63 and 64, respectively, of any suitable material such as aluminum, copper, steel, their alloys and the like. The faces of strips 61 and 62 which are to be juxtaposed are in some instances subjected to scratch brushing by the rotary brushes 65 and 66, respectively; and to the scratch brushed surface of one of the strips, namely 61, there is applied parallel spaced stripes 75 (FIGURE 6) of weldpreventing material by means of a grooved applicator roll 67 operating from its slurry 68 of weld-preventing material. The adherent, thin layer of material 75 is then dried by any suitable means, such as the heater coil 69, after which the component strips 61 and 62 are brought into contiguity at the pinch rolls 70 just prior to entry of the assembly into the heating furnace 71, where the assembly is heated to a desired pressure welding temperature. The assembly of component strips and weld-preventing stripes 75 issuing from the furnace is then passed between the bonding rolls of the mill 72. This accomplishes a pressure weld between component strips 61 and 62 at the intervening areas between the weld-preventing stripes 75. Next, specially bonded and laminated sheet 74 issuing from the mill 72 is cut up into individual tube strips 76 by passage between slitter rolls 73. Each of the tube strips 76 is then subjected to a swaging or forging operation between the grooved work faces of die blocks 77 and 78 so as to provide the integrally finned tube sheet blank 79.

The individual finned tube strips produced may then be erected to the hollow form in any suitable manner. Injection of internal fluid pressure intothe stratum of parting may be employed; or a suitable tool such as a shaped and pointed mandrel may be forced down the lamination of each strip, particularly when in relatively short lengths, to accomplish opening of the internal fluid passageway.

The individual finned tubes may be assembled together as shown in FIGURE 9 to make a radiator core. In this instance each tube 80 is provided with a series of opposing fins 85 and 86 on the opposite faces as in the previous embodiments. However, each tube 80 is also provided with a special construction at each end to adapt the tubes to be assembled with the orificed header plates 87 and 8-8 of the core. At each end there is provided an outwardly extending flange or hilt 89 against which either plate 87 and 88 may be seated. The end structure of the tubes 80 is likewise characterized by an end portion 81 free from any fins so as to permit the ends of the tubes 80 to be passed through suitable openings in the header or end plates 87 and 88.

In FIGURE there is shown a strap type of heat exchanger 90 made in accordance with this invention. The unit is provided with a single heat exchanger fluid passageway 113, one end of which at 91 is constructed so as to enable inlet connection to be made with ordinary tubing 111. At the other end 92 the unit is similarly constructed for connection with outlet tube 112. Between these ends there are provided on the exterior of unit 90 a series of transverse integral fins such as 95 extending all the way across the unit 90 including the lateral edges 93 and 94.

To produce the external fins in this embodiment, there may be provided the swaging rolls 97 and 98 of FIGURE 11 instead of the reciprocating forging dies described hereinbefore. Rolls 97 and 98, the latter of which is flanged on both ends, have a peripheral construction suitable for manufacturing the fin structure and strip of FIGURE 10. It will be understood that the roll periphery may have grooved or toothed forms identical or similar to the working faces shown in FIGURES 7 and 8. Each roll is provided with protruding forging teeth or lands, such as teeth of roll 97 and teeth 106 of flanged roll 98. These teeth are designed to come into registry in opposition to each other at the roll bite at which the roll spacing is adapted to accomplish the desired swagin'g and flow of metal needed to make the fins. The roll 97 and the roll 98 is each free from the forging teeth over a portion of their peripheries such as 103 and 104, respectively, so that these recessed portions of the periphery may leave the ends 91 and 92 of the unit of FIGURE 10 free from fins. At this recessed portion of the rolls 97 and 98 there is provided a pair of registerable pinch off sharp protrusions such as 101 and 102, respectively. When these come together into substantial contact and registry, desired measured portions of the strip are cut apart from each other.

Among the advantages of the construction of this tubing is that not only are the tube walls desirably thinned and provided with heat transfer elements for more efficient heat conduction but also that the walls of the tubing itself are stiffened by the cold formed ribbing thus increasing the safety factor of the tubing and its resistance against undesired deflection under high internal pressure. The lateral edges have the effect, especially when of relatively massive cross section of a longitudinal stiffening and shape holding member. This adapts the tubes for being formed to various substantially self-retaining heat exchanger core tube configurations. The metal of the tube in the fins and adjacent the fins is most severely worked and, therefore, admirably suited to necessitate undesired deflection of the tube walls. The cross sectional shape of the tube, which in general is lenticular or oblong and relatively flat, is advantageous for many heat exchanger structures.

While embodiments of this invention now believed to be preferred are disclosed herein, it is to be understood that other embodiments, changes and modifications may occur to those skilled in the art without departing from the spirit and scope of this invention as set forth in the appended claim.

What is claimed is:

A length of airfoil shaped tubing comprising a pair of longitudinally extending tube side walls integral with each other at their lateral edge .portions and spaced apart intermediate said edges, one of said edge portions constituting the leading edge of the tubing while the other edge portion constitutes the trailing edge, and a series of external, integral transverse fins extending from said leading edge and at least one of said side walls, said fins extending outwardly in airfoil profile to a maximum extension adjacent said leading edge and to a minimum extension adjacent said trailing edge.

References Cited by the Examiner UNITED STATES PATENTS 1,91 1,403 5/ 1933 Soverhill 177 X FOREIGN PATENTS 595,024 ll/ 1947 Great Britain.

ROBERT A. OLEARY, Primary Examiner.

JAMES W. WESTHAVER, Examiner.

A. W. DAVIS, Assistant Examiner. 

